Naturalistic Pantheism might best be understood through the teachings of Spinoza and Taoism historically, and the Universal Pantheist Society (UPS) and the World Pantheist Movement (WPM) today.
Although the UPS is the older of the two, it has seen decreased activity in recent years. The WPM (founded by former UPS vice-president Paul Harrison), on the other hand, has expanded considerably due to its promotion of 'Scientific Pantheism', which many critics submit is essentially nothing more than "atheism for nature lovers". This charge seems to stem from the fact that 'scientific pantheism' is not only naturalistic, but avowedly materialistic as well, with little tolerance for any reference to traditional theological concepts. Despite a history of controversy ignited by the WPM's appearance as sect within the UPS and its eventual seccession from that organization, the WPM approach has met with some acceptance, even while it may not actually constitute any strict pantheism.
Although the Universal Pantheist Society ostensibly accepts pantheists of all varieties, in practice, it too tends toward the 'modern' (naturalistic) pantheism. To understand this, it must be re-emphasized that the theological concept which the term 'pantheism' was originally intended to describe (the equivalence of the traditional God concept with nature) is considered to be essentially obsolete by many contemporary members of the Naturalistic pantheist community, whose intent in describing themselves as 'pantheist' is chiefly to identify themselves as adherents of a naturalistic spirituality by using an established term. Opponents of naturalistic pantheism and adherents of classical pantheism charge that this constitutes the intentional misuse of terminology, and the attempt to justify atheism by deceptively mislabeling it as pantheism. Some naturalistic pantheists, recognizing this, are willing to concede that the term may in fact be more appropriate for dualism than for themselves, and there is currently some discussion over possible alternative terms for the worldview most commonly promoted as 'pantheism' today.
Naturalistic pantheism places little emphasis on the concept of 'God'. This raises the concern that this is really no longer pantheism at all, but something more like 'spiritual naturalism' or atheism. After all, these critics ask, if you remove the concept of God from your philosophy, what is the purpose using the term pantheism? It is clear from the etymology of the word that it is inappropriatly used in discribing an anti-theist philosophy. In answer to this objection, naturalistic pantheists maintain that the 'pan' prefix (meaning 'all') modifies the 'theism' suffix (meaning 'God') to such an extent that pantheism in fact has little to do with traditional theism.
Classical pantheists and cosmotheists regard this 'modern pantheism' as simply a more reverent and naturalistic form of atheism, since this unusual conception of God is seen as bending the traditional definition so far as to make it meaningless. In the view of some modern adherents, however, the objection to using the historical term 'pantheism' for the naturalistic interpretation of this viewpoint is essentially valid, and these adherents usually admit that the term is maintained only for the sake of convenience if not accuracy.
A typical argument intended to show that the term 'pantheism' remains appropriate for the modern (naturalistic) interpretation thereof is based on the aforementioned fact that the contemporary pantheist sees the term 'God' as a synonym for nature. If nature is equivalent to the theological concept of God, then saying 'all is God' (pan-theism) is the same as saying 'all is nature.' Accordingly, this is the way that many pantheists choose to view the term 'pantheism' - All is nature, nature is All. Pantheism, then, is (in this view) essentially a form of spirituality based on nature rather than on supernatural entities such as deities. Accordingly, it is widely accepted that the modern interpretation of pantheism is essentially naturalistic, and therefore constitutes a form of naturalistic spirituality.
In addition, a number of modern (naturalistic) pantheists further identify themselves as 'mystics,' which only creates another potential source of confusion, although the debate over this has been somewhat less heated than that over other terminology. It is widely (although not universally) accepted that the essence of mysticism within the context of pantheistic thought lies in a 'direct knowledge or a direct experience of God,' which is obviously readily attainable by the pantheist, considering that his or her 'God' is all that exists.
However, general acceptance of naturalistic pantheism has been undermined to some extent by the existence of considerable disagreement within the pantheist community as to whether or not ideas such as 'sprituality' are truly applicable to a naturalistic worldview. Although there has been no clear conclusion that has been reached to date, the rough consensus currently holds that within a pantheistic framework, 'spirituality' can be meaningfully and consistently interpreted as 'the human relation to the numinous', as Carl Sagan and some others have suggested.